Discharge system



March 6, 1956 M. w. SIMS 2,737,612

DISCHARGE SYSTEM Filed Feb. 9, 1953 2 Sheets-Sheet 1 CAPACITOR VOLTAGE AND CURRENT Inventor: Marion W. Sims,

His Attorney March 6, 1956 M. w. SIMS DISCHARGE SYSTEM 2 Sheets-Sheet 2 Filed Feb. 9, 1953 m -Ll .r 3 nT Inventor Marion W. Sims,

His Attorney.

2,737,612 rP tented Ma ,9 5

1 improvedecapaeitor discharge system incorporating the TDISCHARGE 'SYSTEM Miirlbli-"wi sims; Fert wa -neymm; sssignnr to General i-Electric Companyg a corporationof New York f "Application'February 9,"1953;seria1 No". $1 2 5,666 f C lClaims. c1. 315- 177 Thi-s invent-ion* relates to discharge systenis such-as -.;ignition: systems and nibre particuiarly .tti' systems :of the cap'acitor dischargetype. i :1 1 mIt has' b'e'en found that themapacitor diseharge type:of ignition system is desirable for certainra pplications, such asin' aircraft gas turbines; and an*improvedisystemofthis ity'pe' is shown in 'cope'nding applicationserial .No: 299,4'1 6 ifile'd' luly'" 1 7, 1952,- now Patent 2 7 1 7;335 issued September :16; l-955;' in the name of Marion' W Sinisg' Ezra C. Hill: and -Aaro'nIM. Kra'kower; and assignedfto tha'assignee' of the -present 'application. This-*system comprisest a main discharge circuit including a main storage capacitor; *an in- "ductance; i-whi'ch is actuallycthe secondary or a a stepup :transformer, :and the ignition -gap. The .primarywinding of the transformer is connectedtin F a loop circuit withr an 'auxiliary gapi and a triggering capacitoi .J- the'strig'gering capacitor? being connected for chargingzza'cross :the' main capaciton through ar timing resistor; fl herauxiliar yrigap is arrang'ed to break down beforelthei'main ignition szgap and thus discharges Ethel-triggering capacitor :.through. .the ltransformer primary. .This induces aihigh voltage'tinithe secondary win'din'g', breaking downthe ignition gaprsoztha-t th'e :rn'ain capacitor discharges throughnzthe stran'sformer -secondary and"'the 'gap. As pointednoutain :the'rsabovementioned i application? Serial: NO)? 299;451J6, iII0W- "Patent Nu-2,717,335 it is desirable that ithe 'i'esistancezof the inain discharge 5 circuit be kept a's1 flow :asiqaos'sible; The i main :dis'charge circuit isthus anresonantucircuit andwonce .the'main capacitor has'fi'red'; o'sciliationacontinuesp damped OnIy byJthe ignition gap andannavoidablercircuitttlosses, -uxitil 'xth'e original energyr stored :in .the main capacitor: has been dissipated. 1 Capacitor discharge systemsirare" notrestricteditodiigh voltage'circuitsand a typical-110w voltage'isystemrincludes a rnaimst'orage ca'pacitor; an inductance} andz'a'ctrigg'ering gap connected in a loop circuit with an ignition gapdvhich "dbes no't require a .highiioni'zing Woltagepsuchras asurface 'd-ischarge type of gap. ='Here-again ;ater::the ignitibn -gap T is' broken down; a 'resona nt circuitais provided whichwwill Uscillate'tuntil the "energy stored rinothei ma' .zcapacitor has been dissipated i I'n additionccapacitordischarge systems;maybeSutilized "for application other than ignitionffor.'exampleywclding. --In such a system; the stora'ge capacitoriantlran-tinductance are connected across the Welding electrodes,ithusagain producing: an oscillatory circuit after the weldingnarc has been struckf a I lt has been found that-the oscillation of the discharge circuit in a capacitor 'discharg'e system:produces various high irequency 'l'osses" and it iscitherefore rdesir-ableto modifyithe circuit to produce a highcurrentiinductive discharge without oscillation. lnsertion of radditionahre- "'sist'ancedn the discharge CiICllitdSlIlOt practicable:-;since,= by virtue of the high currents-involved, therlosses-therein would 'be disproportionately large-' It 'risnthereforef desir'a'ble to provide means for preventing oscillation-10f the discha'r-ge circuit withoutiintroducing additional: resistance.

An object of 'this invention.isrtherefore to providezan desirablefieaturs -*set forth above. "Further robjects andadvantages or this 'invention will become apparent-and the inverition w'ill be better under- .stood by'referen'ce to thc -following description and the -'accornpanying drawing; and fthe features of novelty which characterize this: invention will be pb'inted out with particularit-y in the claims annexed {to and forming apart of the specification.

Hm-accordance with one emb'odiment of this invention, a capacitor.discharge-system of the type described in the nfotrementioned'*sapplication i' Sei-ial No. *299,416, now :Pate'n't N0. 52;717i335pis: provided. This system comprises aa'main storage capacitor, adapted to be charged 'fromsa source -of directiicurrent, connected in a main discharge circuit with a high voltagesecondary-transr' formeriwinding and andgnition tgaip A'triggering capaci- 101' is provided :connected' for; charging through a'tirning "resistanceracross iherrmainircapacitor andwalso connected :in :atclcsedloop circuiti withi'a triggering gaprand the'low avolta'geprimaryrwinding ofisthe transformer. The charge 'sacrossrtheidriggering :capacitonzcausesathe triggering gap 'itoibreak dowmbfeforeithe maind'gniiion gap thus discharg- .dfigqthertriggering-coapacitor:through thertransformer pricmary winding: Thisiinduces: avhigh: voltage ;in the transf0nner sec0ndany breakingedowm the: ignition gap sothat ethei main. -;capacitorrrdischarges:ithroughflxthe. transformer .isecondary-r and 'itheiigapz :Irizorderwto prevent oscillation dfi'rthe: mainidischarge Fcircuit; a-zunilateral. current -con- :ducting: deviceisconnected:acrossthe-main capacitor. i'fhis deviceaeshort CiIZiJitS rlh :main capacitorat .-the iinstanteits zvoltager :goes tthroughethedirst J'ZBIO after dis- :ehargeihus providing-ae-high:currentinductive discharge :and: :preventingrthm arc p,owcr. -,-fron1 going. through zero wnnt-ilfitherdischarge is completed. 7 In accordance with another embodiment of this inwention a low qvoltageecapacitor gdischarge ignition sys- ;-tem-z ;is provided comprising--a-,storage; capacitor adapted s-IO'. beecharged from a source of, direct current and conanectedt in seriesrw-itheanainduetance anda triggering gap racross an .ignitionagap. -;-In. order to preventoscillation ofifithisitcircuinaa unilateral current conducting deviceis ..connectedgaer.ossthexapacitor, again short-circuiting the capacitor; at lthe. instantits -voltage goes throughthe first zero after discharge-therebygproviding a high current in- -ductive discharge. v

.2Aat=further embodiment ,of tthist invention provides a :capaciton-discharge welding;..circuitcomprising a storage ;.ca pacitor adapted-tobe-connectedacross .a source of .di- :rect current. and :being tconnected in series with, an in- -ductance.-and;.thewelding:electrodes. .Qscillation of .the

. rcircuit afterwthe welding-.arcxhas, beenstruck is again ,-prevented .byaunilateral current conducting. device connected across :theistoragecapacitor.

*- .Jn :the:drawing, Fig. 1,.is a schematic. circuit diagramof .the improved.capacitondischarge ignition system of this invention;

t-: .Fig.. 2illustrates;typicalyoltage. and current curves of the system .of: .the. aforementioned. application Serial No. {299,416:cornparedwithQthe current. curve .for theim- .proved system. of. this invention;

irFigntSMis-aschematiQ circuit. diagram of a low voltage capacitor. discharge ignition,.systemlpinuaccordance with ,this invention; and

Eig. 4 schema ic l y. HStIatQS. a capacitor discharge Qweldingacircuit. incorporating this. invention. l-aRefei-ri ng :now. to Eig.;1,,.there., is ,shown, a main .catpacitor.lhconnectedtbetwccn, input (terminal. 2, andcomamonaterminalfi. tsT-erm nalsi and. Swam -adapted to, be connectedton source of direct .cu i ent a'sby lines 4. and 5 ,-t.-itnb eingi understood ,that :,,a voltage; stabilizing circuit rofiathe tiypc ashqwli.H nwthetii qtflnwtiqn pplication Serial No. 299,416, now Patent No. 2,717,335, may be utilized as a source of unidirectional current.

Main storage capacitor 1 is connected in a main discharge circuit, shown by heavy lines, including high voltage secondary winding 6 of ionization transformer 7 and ignition gap 8. More specifically, high voltage secondary winding 6 of transformer 7 is connected between input terminal 2 and output terminal 9. The ignition gap 8, which may be any suitable spark discharge device and does not form a part of this invention, is adapted to be connected across output terminal 9 and common terminal 3.

In order to trigger the discharge of main capacitor 1, triggering capacitor 10 is provided serially connected with timing resistor 11 across input terminal 2 and common terminal 3. A sealed trigger gap 12 is then serially connected with the low voltage primary winding 13 of transformer 7 across triggering capacitor 10 forming a closed loop circuit.

With the system as thus far described, upon application of a direct current voltage across input terminal 2 and common terminal 3, charges build up upon main capacitor 1 and triggering capacitor 10, the charging of capacitor 10 being slowed to the desired extent by the requirement that the charging current flow through timing resistor 11. When the voltage across triggering capacitor 10 reaches the breakdown value of sealed trigger gap 12,

which is substantially lower than the voltage required to break down ignition gap 8, trigger gap 12 arcs over thus applying the full voltage of triggering capacitor 10 to the low voltage primary winding 13 of transformer 7. This results in a high voltage being induced in high voltage primary winding 6 of transformer 7 causing the main ignition gap 8 to break down, thus completing the main discharge circuit comprising the main storage capacitor 1, the high voltage secondary winding 6 of transformer 7, and ignition gap 8. Main capacitorl thus discharges through high voltage secondary winding 6 of transformer 7 and the ignition gap 8. w

Referring now to Fig. 2, the curve shown by the solid line 14 represents the configuration of the discharge current flowing in the capacitor 1 of the circuit as thus far described and the dashed line 15 similarly represents the configuration of the voltage across capacitor 1. It can be readily seen that the circuit as thus far described is a simple series resistance-inductance-capacitance resonant circuit with an initial charge on the main capacitor 1. When capacitor I initially discharges, the current in the circuit builds up as shown by initial portion 16 of current wave 14 while its voltage, as shown by initial portion 17 of voltage wave 15 goes down. The voltage across capacitor 1 reaches zero as the current flow reaches a maximum and the current flow would thus ordinarily cease were it not for the inductive effect of transformer secondary winding'6 which tends to keep current flowing in the same direction. The inductance of winding 6 thus charges capacitor 1 in the opposite polarity and the oscillation continues, as shown by curves 14 and 15 until the unavoidable losses in the circuit have completely dissipated the initial charge on main capacitor 1.

As pointed out above, it is desirable to eliminate the oscillationof the main discharge circuit without inserting additional resistance. To accomplish this objective, a unilateral current conducting device 18, such as a selenium cell, is connected across main capacitor 1. The unilateral current conducting device or blocking rectifier 18 thusv short circuits the main capacitor 1 at the instant its voltage goes through the first zero thus preventing oscillation and producing a high current inductive discharge. Referring again to Fig. 2, upon initial discharge of main capacitor 1, the current 16 will again rise as the voltage 17 decreases. When the voltage first reaches zero, however, the presence of, blocking rectifier 18 preventscapacitor 1 from being charged in the'opposite direction and the circuit becomes a simple resistance-inductance loop with secondary winding 6 of transformer 7 maintaining the current flow until it is dissipated by the other losses in the system. Thus, a high current inductive discharge, as shown by the heavy line 18 in Fig. 2 is produced preventing the power in the arc of ignition gap 8 from going through zero until the discharge is completed and eliminating the inherent high frequency losses produced by oscillation in the circuit.

It will now be apparent that the use of a unilateral current conducting device connected across the capacitor may be used in any circuit intended to transfer the energy stored in a capacitor through an inductance to some dissipative element. The use of the unilateral current conducting device permits the capacitor energy to be transferred to the inductance without oscillation thus permitting a single inductive discharge of high intensity. Thus, this invention is not restricted to high voltage capacitor discharge ignition circuits as hereinbefore, described, but may also be used with other capacitor discharge ignition circuits, for example, a circuit having a gap which does not require a high ionizing voltage, such as a surface discharge type gap.

Referring now to Fig. 3, there is shown a low voltage capacitor discharge ignition system having a storage capacitor 19 connected across input terminals 20 and 21 which are adapted to be connected to an external source of direct current through lines 22 and 23. Input terminal 21 is connected to output terminal 24 while inductance 25 and sealed triggering gap 26 are serially connected between the input terminal 20 and output terminal 27. A suitable ignition gap, such as a surface discharge type gap 28, is adapted to be connected across output terminals 24 and 27. It will be readily seen that after breakdown of the ignition gap 28, a resonant circuit is provided and in order to prevent oscillation of this circuit, a unilateral current conducting device 29 is connected across main capacitor 19.

Referring now to Fig. 4, there is shown a capacitor discharge welding circuit having a main capacitor 30 connected across input terminals 31 and 32 which are adapted to be connected across a source of direct current by lines 33 and 34. Input terminal 32 is connected to output terminal 35 and inductance 36 is connected between input terminal 31 and output terminal 37. Welding electrodes 38 and 39 are adapted to be connected across output terminals 35 and 37. It will be readily seen that when electrodes 38 and 39 are brought into contact with work 40, the circuit is completed and that a resonant circuit is again provided. .Here again, in order to prevent oscillation of this circuit and to provide high current inductive discharge, a unilateral current conducting device 41 is connected across a storage capacitor 30.

It will now be seen that this invention eliminates the undesirable oscillation in a capacitor discharge system producing a desirable high current inductive discharge with a resultant increase in efficiency of the system and ignition ability of the working gap.

While I have shown and described particular embodiments of this invention, further modifications and improvements will occur to those skilled in the art, for example, the oscillation eliminating feature of this invention could be applied to any of the circuits disclosed in the aforementioned application Serial No. 299,416, now Pat. No. 2,717,335. I desire it to be understood, therefore, that this invention is not limited to the particular form shown and I intend in the appended claims to cover all modifications which do not depart from the spirit and scope of this invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. A capacitor discharge ignition system comprising, in combination, a main energy storage capacitor adapted to be charged from a source of unidirectional voltage, a triggering capacitor connected to be charged through a resistor by said source, a voltage step-up transformer having a low voltage primary winding and a high voltage secondary winding, a circuit completing triggering device connected to discharge said triggering capacitor through said low voltage primary winding when the voltage charge on said triggering capacitor attains a predetermined value, said transformer having at least said secondary Winding connected directly in series with said main capacitor forming a discharge circuit, an ignition gap connected in said discharge circuit, and a unilateral current conducting device connected across said main capacitor whereby oscillation of said discharge circuit is prevented.

2. A capacitor discharge ignition system comprising a main energy storage capacitor adapted to be charged from a source of unidirectional voltage, a triggering capacitor connected to be charged through a resistor by said source, a voltage step-up transformer having a low voltage primary winding and a high voltage secondary winding, a

10 cillation of said discharge circuit is prevented.

References Cited in the file of this patent UNITED STATES PATENTS 15 2,235,385 Rava Mar. 18, 1941 2,310,092 Knowles Feb. 2, 1943 2,497,307 Lang Feb. 14, 1950 2,503,054 Laird Apr. 4, 1950 2,551,101 De Benham et a1 May 1, 1951 

